Programmable controllers have been used to control various kinds of machines such as automatic machines in factories and public facilities and familiar machines. The programmable controllers include a mechanism to receive information from sensors of the machines as input information for calculation and output command values to actuators of the machines.
A substantial difference in configuration between the programmable controllers and general-purpose PCs is in that the programmable controllers include a special LSI for operation commands to operate an MPU with a low clock frequency, and thus do not rise to high temperatures unlike the general-purpose PCs. Further, they do not incorporate fans having short product life. Therefore, typically, severe restrictions are imposed on the sizes of built-in programmable controllers.
As described above, compared with the normal general-purpose PCs, the programmable controllers are required to have a higher operating environment temperature, and a real-time performance (to terminate a calculation within a given period to complete input/output to/from an I/O) and to be a smaller in size.
Further, the smaller the programmable controllers in size, the wider variety of applications to which they are applied. Because of this, in recent years the downsizing of the programmable controllers has progressed.
However, the programmable controllers need to incorporate an emergency stop switch and an LED that indicates their states. In a small size programmable controller, operation switches have to be arranged with a narrower interval, therefore, it becomes difficult to operate the switches from outside.
Further, conventionally a method of switching an operation to be executed has been proposed. However, it is difficult for users to perform a switching operation with a small operation element, and users may unintentionally touch the operation element and cause an erroneous operation.